Lamp control circuit



April 28, 1959 R. L. FREEMAN ET AL 2,884,

LAMP CONTROL CIRCUIT Filed Dec. 22, 1955 VOLTAGE REGULATOR :2 7 l9 sOuRcE L VOLTAGE 57 REGULATOR 75 72 A o as OONTROL --o' 2 75 VOLTAGE VOLTAGE 83 34 REGULATOR ii 74 7! 4 sOuRcE F 3 L CONTROL VOLTAGE 37 854:

VOLTAGE REGULATOR 97 FIG.4 2 no m r {99 Inventors SOURCE ROBERT FREEMAN and CHARLES H. OuRREY 385???? by Attorneys United States Patent @fifice I 2,884,567 Patented Apr. 28, 1959 LAMP CONTROL CIRCUIT Robert L. Freeman, Glenview, and Charles H. Currey, Palatine, Iil., assignors to A. C. Nielsen Company, Chicago, 111., a corporation of Illinois Application December 22, 1955, Serial No. 554,693

3 Claims. (Cl. 315-208) The present invention relates to lamp control circuits, and more particularly to circuits and methods for controlling the energization of lamps employed in photographic recorders of the type described in Currey application, Serial No. 381,344, filed September 21, 1953, and assigned to the same assignee as the present application.

Film type recorders generally employ a record receiving medium or film consisting of a supporting member having a light sensitive layer on one surface thereof. Selected portions of the sensitive layer are exposed to a controllable source of light in accordance with intelligence supplied to the recorder. In many applications of film recortlers, such, for example, as the wave signal receiver monitoring apparatus of the above-mentioned Currey application, the light sensitive layer is provided on a flexible tape which is continuously moved past the light source, which light source is periodically switched on and off to provide a plurality of discrete marks on the recording medium at selected positions thereon. In such applications it is not uncommon for the source of light to be alternately switched from an exposing to a nonexposing condition at very frequent intervals, such, for example, as two-second intervals throughout extended periods of time.

It has been found to be desirable to utilize as the light producing source an electric lamp, and to selectively change this source from an exposing to a nonexposing condition by switching the lamp between conditions of energization and nonenergization. It has been found that cold-cathode gaseous type lamps, such, for example, as argon lamps, do not suffer an appreciable shortening in life under the severe intermittent operating conditions encountered in the prior art switching arrangements. However, argon lamps or other gaseous type lamps have not been altogether satisfactory because of the high initial cost thereof and, moreover, because the intensity of the light produced by these lamps fluctuates considerably with time and varies from lamp to lamp. On the other hand, incandescent lamps which include a heated filament located in an evacuated transparent or translucent envelope or one filled with inert gas provide a rela tively constant and uniform light throughout a substantial portion of their lives. Moreover, such incandescent lamps are inexpensive in ititial cost as compared to the cost of argon lamps which must be pretested 'by film ex posure that reveals many rejectable ones. The ratio of the total costs is approximately one hundred to one. However, because of the rapid and frequent switching of the lamps of film type recorders between On" and Olf conditions, it has been found that the lives of incandescent lamps when used in such application prohibitively short because of the mechanical s. och suffered by the rather brittle filament assemblies because of thermal expansion and contraction.

Accordingly, it is a principal object of the present invention to provide a new and improved arrangement for providing a stable and uniform light source suitable for use in a film recorder; k

It is another object of the present invention to provide a new and improved circuit for controlling the periodic energization of a lamp so as appreciably to increase the life of the lamp.

A further object of the present invention is to provide a new and improved circuit for controlling the energization of an incandescent lamp.

A still further object of the present invention is to provide a new and improved lamp euergization circuit which may be used for appreciably increasing the life of incandescent lamps used in film recorders.

Another object of the present invention is to provide a new and improved method of exposing a photographic film.

Still another object of the present invention is to provide new and improved apparatus for producing a record on a light sensitive medium.

Briefly, and in accordance with one aspect of the present invention, the above and further objects are realized by providing a lamp energization circuit in which the lamp is provided at all times with at least a small energizing current and is provided with an energizing current of greater value when actinic light is desired. In accordance with another aspect of the invention, a lamp to be controlled is connected in series with the primary winding of a transformer and the load impedance on the secondary winding is adjusted thereby to control the energizing current through the lamp.

Further objects, aspects and advantages of the present invention will become apparent with a reading of the following detailed description with reference to the accompanying drawing, in which:

Fig. 1 is a schematic circuit diagram of one embodiment of the present invention;

Fig. 2 is a schematic circuit diagram of another embodiment of the invention;

Fig. 3 is a schematic circuit diagram of still another embodiment of the invention; and

Fig. 4 is a schematic circuit diagram of yet another embodiment of the present invention.

In most, if not all, digital or data recording devices in which a photographic film is selectively exposed by means of light, it is desirable that after development of the film by a suitable process the density of the exposed areas beconsiderably greater than the density of the nonexposed areas. Moreover, when light beam and photocell equipment is provided for interpreting or reading information contained on photographic film, it is important that the density of the nonexposed areas he a minimum so that the greatest change in photocell voltage is obtained between nonexposed and exposed areas. In order to effect optimum densities, it has been the practice in the prior art film recorders to cause a lamp to be switched between fully On and fully OE conditions to provide selected exposed and nonexposed portions of the film. We have found, however, that when incandescent lamps are switched completely On and completely Off at a rapid rate, the lives of the lamps are materially reduced, but if the filaments of the lamps are maintained in a warm condition of 600-1000 degrees Kelvin during the so-called Off condition, the shock is reduced when the excitation is increased to fully On, and the lives of the lamps approach that which would be expected under normal continuous operating conditions. At filament temperatures under 1000 degrees Kelvin, the energy radiated is mostly in the red and infra-red region where most film emulsions and some in particular are rather insensitive. Therefore, in order to provide optimum film densities while at the same time maintaining the lamp in at least a warm condition at all times, we have achieved good results by utilizing so-called bluesensitive or non-color sensitized photographic film which is substantially insensitive to the color of light which is radiated by-an-incandescentlamp when it is energized with a small warming current, but sensitive to the color of light which is radiated thereby when the lamp is fully energized to the extent that-the' filament temperature is about 2800 degrees Kelvin. One example of a suitable combination of a lamp and photographic film which enables long lamp life while providing proper'densities is a type 47, 6-volt, tungsten filament incandescent lamp and Eastman 7302, blue-sensitive film, which film is sensitive to light within the blue-violet and ultra-violet region and insensitive to light in the red and yellow region. Referring now to the drawing and particularly to Fig.

of the present-invention, generally designated at 10, which is shown as being used as thelight source of a film type recorder. As illustrated, the circuit 10 includes a transformer 12 having a primary winding 13 and a secondary winding 14. To insure a uniform supply winding being connected to the other output terminal of the regulator 16. It may thus be seen that the value of the voltage which is provided across the lamp 21, and

hence the current therein, is dependent upon the exciting current of the primary winding 13 of the transformer 12 and upon the impedance of the load connected to the secondary circuit of thetransformer 12.

' As is known in the art, when the energization current in an incandescent lamp having, for example, a tungsten filament is increased, the intensity of the light emanating therefrom is increased. It is also known that the actinic level of light produced by such a lamp increases with an increasein the lamp energizing current at a substantially greater rate than does the over-all intensity of the light produced because the spectrum of the lamp shifts from the red towards the blue-violet. As a result, by utilizing a photographic film which is particularly sensitive to more actinic blue-violet light, the density of the exposed areas'of the film and the density of the unexposed areas of the film are suitable for use with automatic photoelectric reading devices towhich are supplied record films from a large number of film recorders even though a small current is provided in the lamp filament at all times.

1 thereof, there is shown the lamp energization circuit "In order to control the energization current supplied to the'lamp 21 so that the lamp may be selectively switched between actinic and nonactinic light producing conditions while maintaining at least a small current in the lamp 21 at all times, a switching circuit including a "suitable electron discharge device 25, illustrated as the well-known thyratron, is provided for controlling the impedance of the secondary circuit of the transformer 12, thereby to control the current value in the lamp 21. As shown, a full-wave rectified alternating potential for the plate voltage supply for the thyratron 25 is obtained from a full-wave rectifier 24, defined by unidirectional impedance devices 26 and 27 connected in circuit with the'primary winding 14 of the transformer 15. The i ating direct current output of the full-wave'rectifier s applied to the plate circuit ofthe thyratron 25 through a maidmum current limiting resistor 45. To provide the desired cathode bias, the pulsating-direct current output 'offth'e full-wave rectifier 24 is supplied to a voltage {divider comprising serially connected resistors 28, 29 and 30, resistor 30 being connected by an adjustable tap selectively to control themagnitudeof the cathode bias.

A suitable bypass condenser 31 is connected across resistor 30 for bypassing alternating currents toground and for filtering out the pulsating components of the rectified voltage to provide a steady D.C. cathode bias. The steady D.C. cathode bias insures that the cathode potential will be maintained above a certain critical level that prevents anode discharge in the presence of zero grid control signals or of small spurious grid signals. In order to adjust the warming value of current in the lamp circuit, there. is provided a variable resistive impedance 32, which is connected across the primary winding 13. With the above-described arrangement, it will be seen that when the anode-to-cathode circuit of the thyratron 25 is conductive, the impedance provided across the secondary winding 14 is considerably reduced thereby causing a corresponding decrease in impedance reflected across the primary circuit of transformer 12 with a resultant increase in the current in the lamp 21. By choosing the .value of .resistor'45 and thyratron operating condition and by adjusting the resistor 32 the current level flowing through the lamp 21 can readily be controlled to fall within a desired range both when the thyratron 25 is rendered conductive as well as when nonconductive.

To supply a control voltage to control electrode 25a of thyratron 25 to render the latter conductive, there is provided a suitable source of control voltage for encrgizing the lamp circuit similar to the source of signals from the commutator switch shown in Krahulec application Serial No. 147,302, filed March 2, 1950, Patent No. 2,838,359, or in Currey application Serial No. 381,344.

filed September 17, 1953, both applications being assigned to the same assignee as the instant application.

For simplicity, this source is designated schematically by the reference numeral 43 and is connected to control electrode 25a through resistor 40. The nature of the voltage from this source might be alternating voltage of power supply frequency and of about 10 volts magnitude.

As will be clear from the above description to those skilled in the art, when a positive excursion of voltage of suflicient magnitude to overcome the cut-01f effect of the cathode bias voltage on the thyratron 25 is supplied from the source 43 during the time that the thyratron anode is sufiiciently positive with respect to the thyratron cathode, an anode-cathode discharge of the thyratron takes place, and the current in the lamp 21 is increased by the reduced impedance reflected across the primary circuit.

The resistor 32 is adjusted and the other parameters chosen such that when the thyratron 25 is nonconductive only a negligible amount of actinic light is radiated from the lamp 21, and when the thyratron is conductive a substantial amount of actinic light'is produced. In a device built in accordance with Fig. 1, it has'been found that good results to properly expose blue-sensitive film were obtained when the energization voltage of a type 47 tungsten filament lamp such as 21 rated at 6.0 volts, 0.15 amperes is switched between 0.07 amperes and 0.135 amperes by switching the applied voltage from about 1.5 volts to 6.0 volts.

In view of the detailed description included above, the operation of the arrangement disclosed in Fig. 1, which is at present considered the preferred embodiment of the present invention, will readily be understood by those skilled in the art. The resistor 32 is first adjusted to give a desired value of warming current in the lamp 21; this value should be such that the density of developed film for areas exposed to the lamp under warming current conditions is only about 0.1 greater than that for totally unexposed areas. The cathode bias is then set by adjustment of resistor 29'so that the thyratron current is zero with no control signals from source 43 and is a desired value in the presence of control signals.

Following the desired calibration, the circuit is ready to function. When the thyratron 25 is nonconductive, the lamp current'is determined bythe current; through resistor 32, the primary exciting current and the reflected secondary load caused by resistors 28, 29, and 30. These factors will cause a current i.) flow through incandescent lamp 21 of suchlow magnitude as to be incapable of producing sufficient actinic light to cause significant film exposure. However, the filament of the lamp is kept warm at all times to promote long lamp life. When the thyratron is rendered conductive, the current through the lamp 21 is increased by virtue of the low impedance of this branch of the secondary circuit. This decreased impedance of the secondary circuit of the transformer 12 reflected into the primary circuit causes a great increase in the amount of actinic light produced.

By virtue of the fact that the output of the rectifier 24 is unfiltered, it will be apparent that the plate voltage reaches Zero twice during each cycle of the supply voltage from the voltage regulator 16, and obviously the thyratron 25 is rendered nonconductive at these instances regardless of the control voltages on control electrode 25a. The source 43 of control voltage will normally comprise the alternating current voltage similar to that of the source connected at terminals 18 and 19. By using the unfiltered rectified plate voltage for the thyratron 25, it is immaterial whether the source of pulses 43 is in phase or out of phase with the voltage connected to the terminals 18 and 19, and the thyratron current pulses will cease whenever the control voltages become substantially zero.

From the above description it will be appreciated that very long lamp life is obtained for the incandescent lamp 21, since a warming current flows continually through the lamp and extensive tests have demonstrated a lamp life of many months when switched at the frequent intervals required in a recording operation such as that disclosed and claimed in the abovementioned Krahulec application.

In Fig. 2 of the drawing, there is shown another embodiment of the present invention wherein there is provided a lamp energization circuit for controlling the current in an incandescent lamp 51, which may be identical with the lamp 21 described above. Instead of lamp 51 being in the primary circuit of a transformer in whose secondary circuit there is connected a thyratron as in Fig. 1 of the drawing, the lamp 51 is connected in the secondary circuit of another transformer 59 whose primary winding is also directly connected to the output of voltage regulator 57. As in Fig. 1, the lamp 51 may rapidly be switched between nonactinic and actinic light producing conditions. The circuit 50 includes a pair of input terminals 53 and 54 which are adapted to be con nected to a suitable source of alternating current voltage for application to the primary windings of transformers 56 and 59. Preferably, a voltage regulator 57 is interposed between the source and the transformers 56 and 59. Transformer 59 is connected across the output terminals of the voltage regulator 57 for supplying energization current for the lamp 51 which is serially connected with a winding 60 of a saturable reactor 61 having a control winding 62. In accordance with the present invention, the current flowing in the winding 62 is controlled by a switching circuit including a thyratron 64. The inductance of winding 60 of the saturable reactor 61 in series with the lamp 51 is sufficient to limit the current through lamp 51 to a value low enough not to fog a film such as-23 of Fig. l exposed to such light when the core of saturable reactor 61 is unsaturated. The alternating voltage obtained across the secondary of transformer 56 is rectified by half-wave rectifier 67 and applied to the resistance divider 63a, 63b and to the anode circuit of the thyratron. A capacitance 66 is connected across the resistor 63b in order to filter out the alternating components and provide a steady direct current potential for use as a cathode bias for the thyratron 64. The steady D.C. cathode bias is required for the same reason as for the cathode of thyratron 25 of Fig. 1. The rectifier 67 is purposely used to provide this D.C. bias, and it is immaterial whether unrectified or rectified voltage is applied to the anode of thyratron 64. As in Fig. 1, a source 68 of control voltage, such as the outputs of the commutator switches of the devices disclosed in the above-mentioned Krahulec and Currey applications, is applied to the control electrode 64a of thyratron 64 to control the periods of conduction thereof. However, this source of control voltage must be in phase with the voltage at the secondary of the transformer 56. Because of the inherent characteristic of the control winding 62 of the saturable reactor 61 to cause the current in the anode-to-cathode circuit of the thyratron 64 to decay at a relatively slow rate, a problem is presented of reducing the plate voltage to zero each cycle to render electron discharge valve or thyratron 64 nonconductive. Thus, to insure a substantially zero plate voltage or a plate voltage below the level necessary to sustain conduction of thyratron 64, there is provided a unidirectional impedance in the form of a diode 69 connected across the control winding 62 of the saturable reactor 61 which is polarized in the same manner as thyratron 64 with respect to winding 62. The diode 69 thus short circuits the inductive lagging voltage caused by the slow decay in thyratron anode current at the end of each half-cycle of conduction. At the same time it does not load the anode circuit during the normal conduction period. Therefore, during the half-cycle when thyratron 64 is conducting'and the diode 67 is nonconductive, the anode current of the thyratron flows through the winding 62 so as to saturate, the core of saturable reactor 61 and thus decrease the inductance of winding 60. Since the inductance of Winding 60 is relatively low, a relatively large current will flow in the circuit consisting of the lamp 51 and the energizing potential source comprising the secondary of transformer 59.

The impedance values of the saturable reactor 61 are selected so that the diiference in the values of the current flowing in the lamp 51 between the conductive and nonconductive condition of thyratron 64 is sufficient to provide a satisfactory'record on a photographic film, and the value of current in the lamp 51 during the nonconductive condition is sufficient to insure long lamp life. A precise adjustment of the warming current might be obtained by making the inductance of winding 60 somewhat larger and shunting an adjustable impedance such as a resistor across this winding. Such adjustable resistor would function as resistor 32 in Fig. 1.

In Fig. 3 there is illustrated still another embodiment of the present invention wherein a suitable source of alternating current voltage is connected across a pair of terminals 71 and 72 to which are connected input terminals of a voltage regulator 74 having the output terminals thereof connected across the primary winding 75 of a transformer 76 having a secondary winding 84. As in Fig. 2 of the drawing, the lamp is connected in a circuit separate from the thyratron. As shown, an incandescent lamp 77 similar to the lamps 21 and 51 is inductively coupled to the anode-to-cathode circuit of a thyratron 83 by a transformer 80 having a primary winding 81 and a secondary winding 79. The lamp 77 is connected in series with winding 79 and a source of warming current designated as a battery 78. The thyratron circuit includes the primary winding 81 in the plate circuit thereof. In order to provide a steady direct current voltage for the cathode bias of thyratron 83, a diode 86 is connected between one end of the winding 84 of transformer 76 and the voltage divider circuit comprising fixed resistor 85a and adjustable resistor 85b. The junction between these resistors is connected to the cathode of thyratron 83 and to one terminal of capacitor 87 which serves to filter out the AC. components of voltage. Plate supply voltage for the thyratron is also obtained from the output of diode rectifier 86, although unrectified voltage might also be used. For the same purpose as in Fig. 2 of rthedrawing, a diode 82 is connected across the primary 81 of transformer .80, which primary serves as the plate load impedance of thyratron 83. As in the preceding embodiments, the anode current of the thyratron 83 is controlled by the signal voltage applied to the grid of the thyratron 83 from a suitable source 88 of such signals. It may thus be seen that when the thyratron 83 is rendered conductive, the pulsing anode current flows through the primary 81 and induces a voltage in secondary 79 which excites lamp 77 above the value of current provided in the lamp 77 from the warming current source 78 alone. The source 78 is indicated in, Fig. 3 as a battery, but it will be understood that it may-well be some other source, such as provided by an adjustable resistor that might be connected from the anode of. thyratron, and ground.

I Referring to Fig. 4 of the drawing, there is illustrated another embodiment of the invention wherein an incandescent lamp 90 to be controlled is serially connected with a pair of normally open contacts 91a of a relay 91 across the output terminals of a voltage regulator 93 which is energized from a suitable source of alternating current voltage through inputs 110 and 111. An adjustable resistor 94 is connected across the contacts 91 so that a small amount of current is continually provided in the lamp 90 for maintaining the filament therein in a warm condition. In order to control the energization of the relay 91 so as to control the amount of current in the lamp 90 whereby it may be switched between actinic to nonactinic light producing conditions, a thyratron 96 is adapted to be energized from the secondary winding of the transformer 97, which, in cooperation with a diode 98, provides half-wave rectified energizaition voltage between the anode and cathode of the thyratron 96 and direct current bias for the cathode of the thyratron.

The winding of the relay 91 is connected in the anode to-cathode path of the thyratron 96 such that when the thyratron is conductive by virtue of a positive voltage being supplied to the control grid thereof from a suitable source of signal or control voltage 99, the relay 91 is picked up and the voltage provided between the output terminals of the voltage regulator 93 is connected across the filament of the lamp 90. In this manner, signals from the source 99 are employed to control the amount of light produced by the lamp 90. In view of the detailed description included above, the operation of the arrangement of Fig. 4 will be readily appreciated. However, it should be pointed out that with many types of relays the thyratron 96 will only cut off between the positive pulses of energizing voltage if a diode is connected across the coil 91 to insure that the thyratron anode voltage effectively drops to zero in the periods between the positive excursions of the energizing voltage.

In all of the illustrated embodiments of the invention, thyratrons are employed for switching the energizing voltage of the lamps from one light producing level but it should be understood that vacuum tubes may also be used for this same purpose. v.By using vacuum tubes in place ofthyratrons the diodes connected across the inductance devices in. theplate circuits of the switching tubes -may be eliminated and separate anode and cathode blas .need not be provided. However, when vacuum tubes dominantly red, having only a negligible amount of yellow therein.

- While the invention has been described by a plurality of embodiments thereof, it will be understood by those skilled in the art that changes and modifications may occur to those skilled in the art without departing from the invention and it is intended in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the present invention.

What is claimed as new and desired to be secured by Letters-Patent of the United States is:

1. In a photographic recording system, the combination of an exposure lamp and means for supplying a low I .level of current to said lamp during a first condition of operation of the system and a high level of current to'said-l'amp during a second condition of operation of the system, said means comprising an inductive impedance serially connected with said lamp across a source of alternating current voltage, an electron discharge valve of the gas type, means for coupling the output circuit of said valve to said impedance whereby said valve is energized from said source of alternating current, the magnitude of said impedance being high when said valve is nonconductive and low when said valve is conductive, means for deriving from said source of alternating current voltage pulses of unidirectional voltage, means for supplying said pulses of voltage to the input of said valve only during one of said two conditions, said coupling means comprising a full-wave rectifier whereby proper phasing of the input and output circuits of said valve' is insured.-

2. The combination set forth in claim 1 wherein said inductive impedance comprises a transformer having the primary winding connected in series With said lamp and the secondary winding connected with said rectifier in the anode-tocathode circuit of said valve.

3. The combination set forth in claim 2 which further includes an adjustable resistor connected across said pri mary winding.

References Cited in the file of this patent Stewart May 1, 1934 

